Method of preparing aromatic esters of phosphoric acid



Patented Aug. 15, 1 9 50 METHUD'OF. PREPA nsrnns on rno RING AnoMATIcsPHoRIc non) 1 modernism Jerry asthma, Kingspor-t; assignors to EastmanKodal Companm.

ltochester N. lf a corporation of-New Jersey 7 V This: application,relates to" the preparation of aromatic est'ersof: phosphoric acid: bythereaction. of P205 and the corresponding metaphosphateestersxwitharomatic ethers.

Of late years the neutral esters of phosphoric acid have been found. tobe useful for many purposes, such as plasticizers, lubricants inspinning, starting material-sior insecticides, and the like. Some-of themore commonly known member's of this-class-are triphenyl phosphate,tricresyl phosphate, triethyl phosphate, and tributyl phosphate. Upuntilrecen-tly. the commonly. employed method for preparingthese estershas been by the action of phosphorous oxychlorideand analcohol or phenolresulting in. the formation of hydro-[ chloric acid. There have. beenman patents issued relating to modifications of this reaction in orderto prevent side reactions caused by the liberated hydrochloric acid. As'a consequence; the yields have, been low and the method" has beenexpensive- In-our prior. Patent 2.407i279we have. described" and claimeda. method of preparing" triethyl esters of phosphoric acidin which areaction has been carried out between diethyl ether andPOs in anautoclave. By that method good yields'of triethyl phosphatewereobtained; We have also found .tliat'the aromatic esters of phosphoricacid may be prepared by reacting, an aromatic'ether with. P205 or ametapho'sph'ate at an 'el evate'dtemperature below the boiling pointofthe ether.

One object of our invention is'to provide a process for preparingneutral aromatic esters of phosphoric acid without thedisadvantagesconnected with prior processes whichhave been-employed for theirmanufacture. Another-'o-bj-ect'of' our invention is to providea methodof prepar-- ing triaryl phosphates; A further object o'four inventionis'to" providea process for preparing triaralkylphosphatesr Astilliurtherbbject of our invention'is' to' provide a processorpreparing aromatic esters of phosphoric acid by the use of etherscontainingthe aromatic groups desired in'the-ester products; A stillfurther object of our invention is to provide a process for preparingaromatic esters of phosphoric acid in which P205 may" be employed as thestarting. material. Other objects of our invention will .appear'hereinWe have found that-by using an elevated temperature P205 or a metaphosphate and an aromaticether will react to form-a neutral ester ofphosphoric acidand therebygood yields of phosphoric acid esters maybeobtained, less expensive starting materials may be employed, and thephosphates may be produced in'a more pure state r without the necessityof expensive purifying proin with the" reaction i Nc-Dr'aw-ing';Application -July 14,1947. I Serial No. 760,483

cedures. The products obtained-in accordance with our invention-aretriarylphosphatesor triare allzyl phosphates. 7 With the process-.inaccord ance with our invention the product obtained is sufiicientlypure-- after vacuum: distillation tob'e suitable for mostpurposes'inwhich the product is. employed.

In accordancewith our inventionPz'Oi (or an organic metaphosphate) andan aromatic other are. mixed together in a Well agitated reactionvesseland heated to a-temperature-of I86C; It" is desirable in carryinout the. reactionthat' at least the'l'ess' vigorous portionofthereaction which constitutes the latter'portion tli'ere'o'fbe carriedout at a temperature of -180 Clt'd otbain the productin good yield.

The reaction in accordance without-invention may be carriedcut whetherin thepr'esence or the absence of an" esterification' catalyst: we havefound. however, that when a catalyst employed; the yields are ordinarilygreater'and; therefore; the presence "of a catalyst intheroaotion'mas's' is often desirable.

The aromatic'ethers which may be employed as the starting material inour invention are either the 'aralkyl'ethers, such as dibenzyl"ether, 9w'diphenyl diethyl ether; 5 p diph'enyl diiso propyl ether, anddichlorodienzyl ether; orth'e straight faryl" e-ther's; such, for example, asd-iph-enyl' ether, dicresyl ether, or the like; Better results areordinarily obtained when the ether'is anhydrous although small amountsofmoist-tire have been tolerated i-n'some cases: It is also preferredthat when P205 is employed-i it has not been exposed to-the moisture oi"the" air" to any appreciahle extent. 7

The reaction mass initially may-beatanytem perature within the'range of50-90'"C1, and this temperature is suitable for the first or more" vigo-rousportion of the reaction. After the initiai reaction has subsided,the-reacticn -is-then com pleted' by heating the mixtureat-120-180 C.for several hours, For convenience the reaction may be carried out fromthe beginning at tempera tureswithin the latter range. Afterthevreactioti is completed, the triaryl or triaralkyl I phosphate whichhas been formed is desirabiy removed-from the mass by distillation'orsublimation-using a reduced pressure. Pressures: within the range of 1to 10mm. of: mercury are ordinarily suitable for this. purpose although.pressures either lower or higher than this range'can be employ'edjwithgood effect.

The highest yields; are obtained in our process where the residuefromaprevious batch ismixed" ngredients and again re acted. Thisprocedure aids in recovering additional phosphoric acid ester from aprevious residue. If desired, a previous residue may be employed as thesource of the phosphorus without adding any P205. Instead of, or inaddition to P202, organic meta phosphates may be employed for thestarting material. If an ethyl meta phosphate is employed as thestarting material, a mixed phosphate ester will be obtained, whereas ifa meta phosphate is employed, the resulting product may or may not havea mixture of arcmatic groups in the final product depending upon whetheror not the ether used has the same groups as the meta phosphate used asthe starting material. It is desirable that the ether be employed inexcess For instance, it is desirable that the amount of ether employedbe in a molar amount at least three times the molar amount of the P205.Howfivetimes or even eight or more times the proportion of P205 orphosphorus-supplying material which is employed in the reaction.

Esterifications' have been carried out in accordance" with our inventionin a satisfactory manner, both with and without esterificationcatalysts. Some of the esterification catalysts Which'are suitable foruse in esterifications in accordance with our invention are iodine,sulfuric acid, phosphoric acid, potassium fer-rocyanide, ferricchloride, andzinc chloride.

The following examples illustrate our inven-- tion:

Example 1.100 parts of P205 were slowly added to 309 parts of dibenzylether at 80-90 C. over a period of thirty minutes. The temperature wasthen gradually raised to 135-140 C. over a period of 2 hours therebycompleting the reaction. The mass was subjected to vacuum distillationat ature of 260-340 C. 24 parts of tribenzyl phosphate having a meltingpoint of 61-3 C. were obtained.

fromExample 1. The mixturewas stirred and heated at 110150 C. for twelvehours. The mass was then subjected to vacuum distillation, 1-2 mm. ofmercury pressure, and 1'74 parts of tribenzyl phosphate were obtained.

Example 3.-400 parts of anhydrous diphenyl ether and 50 parts of P202were added to a wellagitated stainless steel autoclave. The temperatureof the mass was gradually raised to 140 C. and was maintained between130 and 150 C. for ten hours. The mass was then subjected to vacuumdistillation mm. of mercury pressure) and a yield of 28.8% of triphenylphosphate based on the P205 was obtained.

Example 4.-255 parts of diphenyl ether were mixed with '71 parts of P205and 0.5 part of iodine in a reaction vessel. The mixture was stirred andheated at reflux for twenty-four hours. Vacuum distillation gave 43parts of triphenyl phosphate.

Example 5 -200 parts of diphenyl ether were mixed with 168 parts ofdiphenyl meta phosphate, and the mixture was stirred and heated at160-170 C. for sixteen hours. Vacuum distillation gave '71 parts oftriphenyl phosphate.

The phosphates obtained in accordance with our invention may be employedfor plasticizing cellulose, derivatives or may be added to various ofthe theoretical amount;

ever; the proportion of ether employed may be 1-2 mm, of mercury using abase heater tempercompositions to decrease inflammability. In theExample 2.396 parts of dibenzyl ether were mixed with 340 parts of theresidue resulting preceding examples other aromatic ethers than thoselisted may be employed, especially ethers of the aralkyl type.

We claim:

1. A method of makingaromatic, esters of phosphoric acid which comprisesheating one molar proportion of P205 with at least three molarproportions of a symmetrical aromatic ether having the formula RORwherein R represents an aromatic hydrocarbon radical at a temperaturewithin the range of 50-180, the total heating being effected for asuflicient time to form a substantial amount of neutral aromaticorthophosphate ester (R0) 2P0, wherein R has the abovedefined meaning.

2. A method of making aromatic esters of phosphoric acid which comprisesheating one molar proportion of P205 with at least three molarproportions of a symmetrical aromatic ether having the formula ROR,wherein R representsan aromatic hydrocarbon radical, first at atemperature within the range 50 to C., and then at a temperature withinthe range 120 to C., the total heating being eifected for a sufficienttime to form a substantial amount of neutral aromatic orthophosphateester (R0)2P0, wherein R has the above-defined meaning.

3. A method of making tribenzyl phosphate which comprises heating onemolar proportion of P205 with at least three molar proportions ofdibenzyl ether, first at a temperature within the range of 50120 C. andthen at a temperature within the range of 120-180 C., the total heatingbeing effected for a sufficient time to form a substantial amount oftribenzyl orthophosphate.

4. A method of making aromatic esters of phosphoric acid which comprisesheating one molar proportion of P205 with at least three molarproportions of a symmetrical aromatic ether having the formula ROR,wherein R represents an aromatic hydrocarbon radical, first at atemperature within the ra'nge50 to 120 C.', and then at atemperature'within the range 120 to 180 C., the total heating'beingeffected for a suflicient time to form a substantial amount of neutralaromatic orthophosphate ester (R0) 2P0, wherein R has the above-definedmeaning, and then subjecting the reaction mass to vacuum distillation toremove the neutral aromatic orthophosphate ester from the mass.

5. A method of making tribenzyl phosphate which comprises heating onemolar proportion of P205 with at least three molar proportions ofdibenzyl ether, first at a. temperature within the range of 50-120 0.and then at a temperature of 120-180 C., the total heating beingeffected for a suflicient time to form a substantial amount of tribenzylphosphate, and then subjecting the reaction mass to vacuum distillationto remove the tribenzyl phosphate from the mass.

DAVID C. HULL. JERRY R. SNODGRASS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Name Date Hull et al Sept. 10, 1946 OTHERREFERENCES Number

1. A METHOD OF MAKING AROMATIC ESTERS OF PHOSPHORIC ACID WHICH COMPRISESHEATING ONE MOLAR PROPORTION OF P2O5 WITH AT LEAST THREE MOLARPROPORTIONS OF A SYMMETRICAL AROMATIC ETHER HAVING THE FORMULA RORWHEREIN R REPRESENTS AN AROMATIC HYDROCARBON RADICAL AT A TEMPERATUREWITHIN THE RANGE OF 50-180*, THE TOTAL HEATING BEING EFFECTED FOR ASUFFICIENT TIME TO FORM A SUBSTANTIAL AMOUNT OF NEUTRAL AROMATICORTHOPHOSPHATE ESTER (RO)3PO, WHEREIN R HAS THE ABOVEDEFINED MEANING.